To help limit flooding damage, several building code organizations and the federal government have promulgated regulations that mandate that buildings with enclosed spaces located below base flood plain levels, such as crawl spaces, must provide for automatic equalization of interior and exterior hydrostatic forces caused by flooding fluids. According to these regulations, flooding fluids must be permitted to freely enter and exit the enclosed spaces. In particular, many of these regulations require builders to install a number of vents in the enclosed spaces.
In addition to the regulations mentioned above, good construction practice embraces the use of vents which can be opened during warmer months to allow for ventilation to permit moisture to escape from crawl spaces, while retaining the ability to close during colder months to prevent the circulation of cold air around exposed plumbing in crawl spaces. Typically, the use of screening and louvers is necessary to achieve both the warm weather and cold weather requirements of proper venting and is required by at least some building codes for openings in foundation walls. As a result, a flood vent must be able to automatically remove the louver and screen barrier when confronted with free-flowing, flooding fluids.